Merge pull request #452 from xiangli-cmu/fix_client-matrix_link

doc(Documentation/libraries-and-tools.md) fix link to clients-matrix

Documentation/libraries-and-tools.md

@@ -46,6 +46,8 @@
 
 A detailed recap of client functionalities can be found in the [clients compatibility matrix][clients-matrix.md].
 
+[clients-matrix.md]: https://github.com/coreos/etcd/blob/master/Documentation/clients-matrix.md
+
 **Chef Integration**
 
 - [coderanger/etcd-chef](https://github.com/coderanger/etcd-chef)